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参数资料
| 型号： | LTC4069EDC-4.4#TRMPBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 电源管理 |
| 英文描述： | 1-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO6 |
| 封装： | 2 X 2 MM, LEAD FREE, PLASTIC, MO-229WCCD-2, DFN-6 |
| 文件页数： | 6/16页 |
| 文件大小： | 192K |
| 代理商： | LTC4069EDC-4.4#TRMPBF |
14
LTC4069-4.4
406944f
Thermistors
The LTC4069-4.4 NTC trip points are designed to work
with thermistors whose resistance-temperature charac-
teristics follow Vishay Dale’s “R-T Curve 1.” The Vishay
NTHS0603NO1N1002J is an example of such a ther-
mistor. However, Vishay Dale has many thermistor prod-
ucts that follow the “R-T Curve 1” characteristic in a variety
of sizes. Furthermore, any thermistor whose ratio of
RCOLD to RHOT is about 5 will also work (Vishay Dale R-T
Curve 1 shows a ratio of RCOLD to RHOT of 3.266/0.5325 =
6.13).
Power conscious designs may want to use thermistors
whose room temperature value is greater than 10k. Vishay
Dale has a number of values of thermistor from 10k to
100k that follow the “R-T Curve 1.” Using different R-T
curves, such as Vishay Dale “R-T Curve 2”, is also pos-
sible. This curve, combined with LTC4069-4.4 internal
thresholds, gives temperature trip points of approximately
0
°C (falling) and 40°C (rising), a delta of 40°C. This delta
in temperature can be moved in either direction by chang-
ing the value of RNOM with respect to RNTC. Increasing
RNOM will move both trip points to higher temperatures.
To calculate RNOM for a shift to lower temperature for
example, use the following equation:
R
Rat
C
NOM
COLD
NTC
=°
3 266
25
.
where RCOLD is the resistance ratio of RNTC at the desired
cold temperature trip point. If you want to shift the trip
points to higher temperatures use the following equation:
R
Rat
C
NOM
HOT
NTC
=°
0 5325
25
.
where RHOT is the resistance ratio of RNTC at the desired
hot temperature trip point.
Here is an example using a 100k R-T Curve 2 thermistor
from Vishay Dale. The difference between the trip points is
40
°C, from before, and we want the cold trip point to be
0
°C, which would put the hot trip point at 40°C. The RNOM
needed is calculated as follows:
R
Rat
C
NOM
COLD
NTC
=°
=
3 266
25
2 816
3
.
.
..
.
266
10
8 62
kk
=
The nearest 1% value for RNOM is 8.66k. This is the value
used to bias the NTC thermistor to get cold and hot trip
points of approximately 0
°C and 40°C respectively. To
extend the delta between the cold and hot trip points, a
resistor, R1, can be added in series with RNTC (see Figure
6). The values of the resistors are calculated as follows:
R
RR
R
NOM
COLD
HOT
=
=
3 266 0 5325
0 5325
3 266
1
..
.
()
0 5325
.
R
COLD
HOT
where RNOM is the value of the bias resistor and RHOT and
RCOLD are the values of RNTC at the desired temperature
trip points. Continuing the example from before with a
desired trip point of 50
°C:
4069 F06
RNOM
8.87k
RNTC
10k
VCC
–
+
–
+
–
+
TOO COLD
TOO HOT
NTC_ENABLE
R1
604
0.76 VCC
0.35 VCC
0.016 VCC
6
NTC
Figure 6. NTC Circuits
APPLICATIO S I FOR ATIO
WU
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相关代理商/技术参数 |
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